Mitigating voltage drop on a 2,000' 480 V feeder

[kwired]

Equipment at 480V is rated for 600V. What is going to be the problem if you are 10% above at 528V unloaded.

Switchgear, fuses, breakers, etc. no problem. That 480 x 120 volt control transformer is now putting out 133 volts, and may be supplying some loads that are on even though the major loads are currently off. Though that may be around the upper end of what may be acceptable, this only gets worse if the 480 volt nominal supply goes up to around 500 when load is minimal, then that extra 10% gets closer to 550 volts, and the 120 volt control transformer may be closer to 145.

 

[MAC702]

It's a 480V feeder. What's it feeding? Might not be just 480/600V equipment.

 

[kingpb]

Switchgear, fuses, breakers, etc. no problem. That 480 x 120 volt control transformer is now putting out 133 volts, and may be supplying some loads that are on even though the major loads are currently off. Though that may be around the upper end of what may be acceptable, this only gets worse if the 480 volt nominal supply goes up to around 500 when load is minimal, then that extra 10% gets closer to 550 volts, and the 120 volt control transformer may be closer to 145.

The 10% above includes the system at 504V plus another 5% to get to the 528V. All within ANSI/IEEE allowable.

 

[Tony S]

A word of caution with over voltage.

We had a new machine installed with 5 VSD’s. It worked fine for the first week, come the following Monday morning every drive had failed. The drive manufacturers replaced all the units under warranty. It happened again the next week and the manufacturer was getting slightly annoyed (putting it mildly). The third week we were told to **** ***!

We knew it had something to do with over voltage during the weekend when our works loading was low. I checked the LV voltage on a Saturday afternoon, instead of 433V we had 475V meaning the 11kV was way too high. Checked other switchboards some were high, others were OK. We had four 20MVA 33/11kV transformers at the intake sub, No1 I couldn’t get the tap changer to do anything. Simple fix, reset the overload on the tap changer drive. End of problem.

 

[kwired]

A word of caution with over voltage.

We had a new machine installed with 5 VSD’s. It worked fine for the first week, come the following Monday morning every drive had failed. The drive manufacturers replaced all the units under warranty. It happened again the next week and the manufacturer was getting slightly annoyed (putting it mildly). The third week we were told to **** ***!

We knew it had something to do with over voltage during the weekend when our works loading was low. I checked the LV voltage on a Saturday afternoon, instead of 433V we had 475V meaning the 11kV was way too high. Checked other switchboards some were high, others were OK. We had four 20MVA 33/11kV transformers at the intake sub, No1 I couldn’t get the tap changer to do anything. Simple fix, reset the overload on the tap changer drive. End of problem.

Solid state equipment seems to be what can't take prolonged overvoltage even if not to any extreme levels. May take some time before failure occurs but once insulation breaks down on something it fails quickly, and PC boards and similar items have very thin clearances and lower designed temp ratings than things like motor and transformer windings.

 

[ptonsparky]

A word of caution with over voltage.

We had a new machine installed with 5 VSD’s. It worked fine for the first week, come the following Monday morning every drive had failed. The drive manufacturers replaced all the units under warranty. It happened again the next week and the manufacturer was getting slightly annoyed (putting it mildly). The third week we were told to **** ***!

We knew it had something to do with over voltage during the weekend when our works loading was low. I checked the LV voltage on a Saturday afternoon, instead of 433V we had 475V meaning the 11kV was way too high. Checked other switchboards some were high, others were OK. We had four 20MVA 33/11kV transformers at the intake sub, No1 I couldn’t get the tap changer to do anything. Simple fix, reset the overload on the tap changer drive. End of problem.

That was an expensive way to determine an overload had tripped. Can I guess you have a different mode of detection now?

 

[dmsv10]

Solid state equipment seems to be what can't take prolonged overvoltage even if not to any extreme levels. May take some time before failure occurs but once insulation breaks down on something it fails quickly, and PC boards and similar items have very thin clearances and lower designed temp ratings than things like motor and transformer windings.

Yes, totally agree, however, we had critical operations not only for the Datacenter but all 1750 people protected by one-ups circuit per office/per cubicle which included all energy management systems with a delicate boards mentioned pneumatic output cards for their handlers everything was on ups that could be. We never had an issue with the speed drives running at 500 volts but prior to US changing that tap as mentioned above, we had an engineering study done based on a thousand KW load on a 2500 KVA transformer so we always had load even on weekends and the voltage on DTaP never exceeded 505vac.
The property referenced above ran for 13 years with said conditions even the size 1 2 and 3 motor starters that were maintained are overly maintained I guess I could say buy constant maintenance and checks voltage checks on coil ohms, contacts changed out to new instead of trying to clean them. When you run a Datacenter you normally have a pretty good budget supported by all levels of management so it would have definitely been a lot more challenging had it been in a industrial plant or standard office building but again the ABB speed drives that we had on all our air handlers the big ones anyways never had any issues with the 500 volts.

Sent from my LGMP260 using Tapatalk

 

[drktmplr12]

considering we have no idea what is connected downstream, electronics, simple starters, lighting ballasts, LED drivers.. whatever...

i would like to reiterate a recommendation made earlier in the thread. step up to 4160 then back to down to 480. eliminates the unknowns and gives you flexibility to adjust taps at the point of use. pad mount transformers are robust machines.

 

[rlundsrud]

Over-voltage can cause some equipment to not operate at all. I had a customer that was in the textiles manufacturing business who's looms stop working when the Poco supply voltage exceeded 500 volts ( I believe a failed Transformer was changed but I'm not sure). The VFD'S of the affected equipment detected this as an over voltage and shut down. It simply required changing the Taps on the Transformer at the facility but they lost production until it was resolved.

 

[Tony S]

That was an expensive way to determine an overload had tripped. Can I guess you have a different mode of detection now?

My fellow engineer died, I retired and the plant was demolished. Problem sorted!

 

[kwired]

Over-voltage can cause some equipment to not operate at all. I had a customer that was in the textiles manufacturing business who's looms stop working when the Poco supply voltage exceeded 500 volts ( I believe a failed Transformer was changed but I'm not sure). The VFD'S of the affected equipment detected this as an over voltage and shut down. It simply required changing the Taps on the Transformer at the facility but they lost production until it was resolved.

When VFD trips on overvoltage it is usually too high of voltage on the DC bus, though that can be a result of too high of input volts, often it is from decelerating too fast or not having a braking resistor if you are frequently decelerating.

Sometimes some equipment can have over/under voltage and phase monitoring equipment and will lock out the machine if not within settings.

 

[rlundsrud]

When VFD trips on overvoltage it is usually too high of voltage on the DC bus, though that can be a result of too high of input volts, often it is from decelerating too fast or not having a braking resistor if you are frequently decelerating.

Sometimes some equipment can have over/under voltage and phase monitoring equipment and will lock out the machine if not within settings.

That's exactly what it was, protection circuitry that locked put the vfd.